Adeel, and 13 co-authors, reported in 2019 that Rare earth elements (REEs) are gaining attention due to rapid rise of modern industries and technological developments in their usage and residual fingerprinting. Cryptic entry of REEs in the natural resources and environment is significant; therefore, life on earth is prone to their nasty effects. Scientific sectors have expressed concerns over the entry of REEs into food chains, which ultimately influences their intake and metabolism in the living organisms.
Objectives
Extensive scientific collections and intensive look in to the latest explorations agglomerated in this document aim to depict the distribution of REEs in soil, sediments, surface waters and groundwater possibly around the globe. Furthermore, it draws attention towards potential risks of intensive industrialization and modern agriculture to the exposure of REEs, and their effects on living organisms. It also draws links of REEs usage and their footprints in natural resources with the major food chains involving plants, animals and humans.
Methods
Scientific literature preferably spanning over the last five years was obtained online from the MEDLINE and other sources publishing the latest studies on REEs distribution, properties, usage, cycling and intrusion in the environment and food-chains. Distribution of REEs in agricultural soils, sediments, surface and ground water was drawn on the global map, together with transport pathways of REEs and their cycling in the natural resources.
Results
Fourteen REEs (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Th and Yb) were plighted in this study. Wide range of their concentrations has been detected in agricultural soils (< 15.9–249.1 μg g−1) and in groundwater (< 3.1–146.2 μg L−1) at various sites worldwide. They have strong tendency to accumulate in the human body, and thus associated with kidney stones. The REEs could also perturb the animal physiology, especially affecting the reproductive development in both terrestrial and aquatic animals. In plants, REEs might affect the germination, root and shoot development and flowering at concentration ranging from 0.4 to 150 mg kg−1
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Conclusions
The authors concluded after reviewing the current status, sources, and potential effects of REEs on plants, animals, humans health that there are also a few examples where REEs have been used to benefit human health. However, still there is scarce information about threshold levels of REEs in the soil, aquatic, and terrestrial resources as well as living entities. Therefore, an aggressive effort is required for global action to generate more data on REEs. The authors prescribe an urgent need for inter-disciplinary studies about REEs in order to identify their toxic effects on both ecosystems and organisms.
The authors concluded that, mainly, they have purposely drawn attention towards potential risks of intensive industrialization and modern agriculture on the release of REEs and their effects on plants, animals and humans health. Finally, this establishes that, REEs in spite of having a few biological benefits, they also render harmful effects on plants, animals and humans. Occurrences of REEs in surface water and groundwater are caused by three main factors;
1) weathering of deposits, 2) leachate of mining areas, and 3) discharges of industrial waste. Justifiable concern has been expressed in the published literature from Europe and U.S. concerning the possible presence of REEs especially Gd in drinking water and their consequent effects on human health.
The authors indicated that the REEs hamper the metabolic system of brain, breasts, lungs, kidneys, bones and testes in humans. REE are claimed to cause shortness of breath, cyanosis, pneumoconiosis, coughing, skin lesions, itching, heat sensitivity and chest pain. Considering these apparent human health issues associated with REEs, the authors claim that it is necessary to investigate toxicological and beneficial mechanisms to improve the basic knowledge about REEs in the healthcare field.
The REEs may also be used to increase the animal's body weight via food supplements. However, they are not considered secure as feed supplements for all animals due to insufficient scientific data. Metabolic system of aquatic organisms might be disrupted by high levels of REEs due to interference in calcium homeostasis. Cultivated lands in the vicinity of mining sites are rich in different REEs, and the REEs derived from mining processes could actually accumulate in agricultural soils and crops. Although, application of REEs could stimulate and promote plant growth and development at low concentrations. However, at higher concentrations REEs may cause serious adverse effects on plants at both physiological (germination, root and shoot length and biomass), and cellular (photosynthesis, senescence) levels.
In the context of above mentioned "facts"?, the following specific points are foreseen for developments in this field:
- Regulatory standards are required to establish the safe threshold concentrations of REEs for soil, environment and living organisms,
- Due to an unprecedented boost in environmental contamination, epidemiological investigations with extensive inclusion of participants are warranted to determine the subsequent health effects of exposure to REEs,
- Domestic and aquatic species sensitive to high doses of REEs should be categorized to avoid life threatening effects,
- Each lanthanum element should be analyzed to clarify its comprehensive toxicity to an organism. Further, there is a dire need to investigate the REEs associated with beneficial or harmful effects in domestic and aquatic animals to avoid economic losses and to support a profitable animal industry,
- Due to different levels of REEs in agricultural crops, scientists are still unable to classify them as toxic or beneficial. Thus, more studies should be performed to unveil the gainful effects of REEs on crops at molecular level, and
- When using REEs via phosphate fertilizer, their long-term effects on soils, plants, water resources, animals, and human health should be considered carefully.
[See video on the subject: https://www.youtube.com/watch?v=ri7fFbrPPjw
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